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Some I-93 commuters may begin noticing buses passing them in the breakdown lane. Here’s why.

MassDOT is beginning a "bus-on-shoulder" pilot that could allow riders to bypass traffic along one of the Boston area's most congested stretches of highway.

A bus traveling on the shoulder of a highway in Minnesota. Metro Transit

Bus-on-shoulder is coming to the Boston area.

Massachusetts officials began running empty buses Wednesday in the breakdown lanes on Interstate-93 north of Boston — between the I-95 interchange and Somerville — to test the feasibility of a longer-term pilot allowing buses with passengers to scoot past traffic one of the area’s most congested stretches of roadway.

In essence, it would create a makeshift bus-only lane on the interstate highway.

The so-called bus-on-shoulder testing will run for three weeks, with MBTA, Merrimack Valley Regional Transit Authority, and the Logan airport express buses using the breakdown lane on I-93 southbound in the morning and on I-93 northbound in the afternoon.

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If the test with empty buses proves safe and successful, state Transportation Secretary Jamey Tesler said the agency will move forward with a pilot that allows those buses to use the breakdown lane when traffic is congested.

“If that passes all the checkpoints we need, we will be able to, in the near term, make a decision to be able to begin this important congestion pilot,” he said during a MassDOT board meeting Wednesday.

According to the MBTA, the Route 354 bus currently experiences 15 to 20 minutes of unreliability per trip due to the traffic along the seven-mile stretch.

“This bus-on-shoulder route would enable the buses to bypass some of this congestion,” Tesler said. “So we are going to continue the testing and look forward to seeing, if that works, initiating this pilot.”

The pilot was first reported last week by StreetsblogMASS, after residents spotted the signage that the MassDOT had put up informing motorists of the pilot. Other vehicles not involved in the field testing remain prohibited from using the breakdown lane. Tesler said Wednesday that the pilot also includes other work, including the removal of rumble strips and deploying portable message boards.

MassDOT agreed to the pilot in a 2020 settlement with the Conservation Law Foundation, after the organization threatened to sue the department over its decision to temporarily open the I-93 southbound carpool lane from Medford to Boston to general traffic. They also received federal approval for a two-year pilot last fall.

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According to MassDOT, the pilot will follow the model of other national bus-on-shoulder initiatives in other areas — from North Carolina to Kansas City to Vancouver.

Buses will only use the breakdown lane when general traffic speeds are below 35 miles per hour. And while using the breakdown lane, they can go up to 15 mph faster than general traffic, up to a maximum speed of 35 mph.

However, officials hinted that they might consider raising the speed limit, depending on how initial testing goes.

“These are the exact questions the pilot test is seeking to answer,” a MassDOT spokesperson said in an email. “Right now, we expect to cap speed at 35 mph, like other pilots nationally. This could change after pilot testing.”

National pilots also generally require buses to return to general lanes if stopped cars or emergency vehicles are using the breakdown lane, and they must yield to vehicles merging onto the highway.

The bus-on-shoulder strategy was first pioneered in the early 1990s by transportation officials in the Twin Cities region in Minnesota, which now has 300 miles of breakdown lanes available to buses. The local transit agency, Metro Transit, says local officials first experimented with the idea and “liked the results.”

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“Bus drivers could stay on schedule, commuters got to work or home faster and ridership increased,” the agency said. “Even better, bus-only shoulders cost a fraction of added lanes.”

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